1) 4*7*10=28*10
4*7=28
2) 5*7*10=7*50
5*10=50
3) 2*8*10=20*8
2*10=20
Составим и решим пропорцию:12 мин. - 5 колец х мин. - 3 кольца12/х=5/3х=12*3/5х=36/5х=7,27,2 мин.=7 мин. 20 с.<span>Ответ: станок-автомат изготавливает 3 кольца за 7 минут 20 секунд.</span>
5/9 + 1 5/7 * ( 4 2/3 - 2 5/8) : 1 3/4 = 2 5/9
1) 4 2/3 - 2 5/8 = 4 16/24 - 2 15/24 = 2 1/24
2) 1 5/7 * 2 1/24 = 12/7 * 49/24 = (1*7)/(1*2) = 7/2 = 3 1/2
3) 3 1/2 : 1 3/4 = 7/2 : 7/4 = 7/2 * 4/7 = 4/2 = 2
4) 5/9 + 2 = 2 5/9
2 - 3 1/7 * (2 - 1 9/11) : 8/21 = 1/2
1) 2 - 1 9/11 = 2/11
2) 3 1/7 * 2/11 = 22/7 * 2/11 = (2*2)/(7*1)= 4/7
3) 4/7 : 8/21= (4*21)/(7*8) = (1*3)/(1*2)= 3/2 = 1 1/2
4) 2 - 1 1/2 = 1/2
2 1/3 + 4 1/10 : (2 7/16 - 5/12) * 5/6 = 4 7/291
1) 2 7/16 - 5/12 = 2 21/48 - 20/48 = 2 1/48
2) 4 1/10 : 2 1/48 = 41/10 * 48/97 = (41*24)/(5*97) =
=984/485=2 14/485
3) 2 14/485 * 5/6 = (984*5)/(485*6) = 164/97 =1 67/97
4) 2 1/3 + 1 67/97 = 2 97/291 + 1 201/291 =
= 3 + 298/291= 3 + 1 7/291 = 4 7/291
4 5/12 - 1 1/2 : ( 2 1/6 + 8/15) * 4/5 = 3 35/36
1) 2 1/6 + 8/15 = 2 5/30 + 16/30 = 2 21/30 = 2 7/10
2) 1 1/2 : 2 7/10 = 3/2 * 10/27 = (1*5)/(1*9)=5/9
3) 5/9 * 4/5 = 4/9
4) 4 5/12 - 4/9 = 4 15/36 - 16/36 = 3 35/36
